Patella bone

The patella is a sesamoid bone embedded within the quadriceps tendon that improves the efficiency of knee extension. Its shape, surfaces, and relations make it a central landmark for clinical assessment and imaging of the knee. A clear grasp of its structure and function supports accurate diagnosis of patellofemoral disorders and safer surgical approaches.

Introduction

The patella, commonly known as the kneecap, is the largest sesamoid bone in the human body and forms an integral part of the extensor mechanism of the knee. By interposing between the quadriceps tendon and the femoral trochlea, it optimizes the line of pull and protects the anterior aspect of the joint. Clinically, variations in patellar morphology, tracking, and soft tissue balance influence pain, instability, and degenerative change.

This section outlines fundamental concepts that frame later discussions on gross anatomy, development, functions, imaging, and clinical relevance. It also highlights the patella’s role as a lever that enhances quadriceps torque during knee extension, thereby contributing to gait efficiency and lower limb stability.

Overview of the Patella

Definition and General Description

The patella is a triangular sesamoid bone situated within the quadriceps tendon proximal to the tibial tuberosity. Its broad superior base anchors the quadriceps tendon, while the pointed inferior apex is continuous with the patellar ligament that inserts on the tibial tuberosity. The posterior surface is covered with articular cartilage and articulates with the femoral trochlea to form the patellofemoral joint.

• Largest sesamoid bone in the body
• Embedded in the quadriceps tendon and linked inferiorly by the patellar ligament
• Anterior surface subcutaneous and protective, posterior surface articular

Historical and Etymological Background

The term patella derives from Latin, referring to a small shallow dish, which reflects its concavo convex profile. Early anatomical descriptions emphasized its shield like role in safeguarding the anterior knee, and later biomechanical studies demonstrated its capacity to increase the moment arm of the quadriceps across varying degrees of flexion.

Significance in Human Anatomy

Functionally, the patella improves quadriceps efficiency by increasing the lever arm during extension, reducing tendon wear, and centralizing force transmission across the femoral trochlea. Its morphology and alignment influence patellar tracking, contact pressures, and susceptibility to pain syndromes. Because it is superficial and easily palpable, the patella serves as a key landmark for surface anatomy, local injections, and surgical incisions around the knee.

Gross Anatomy of the Patella

Location and Orientation

The patella is located anterior to the distal femur within the tendon of the quadriceps femoris muscle. It lies in front of the patellofemoral groove of the femur, where it glides during knee flexion and extension. The bone is positioned with its base superior and apex inferior, forming part of the extensor mechanism that transmits forces from the quadriceps to the tibia through the patellar ligament.

In the extended knee position, the patella sits high and centered over the femoral condyles, while in flexion, it descends into the intercondylar groove. This orientation ensures even distribution of compressive forces across the joint surfaces during movement.

Shape and Dimensions

The patella is roughly triangular in shape with rounded edges. It is thickest at its center and tapers toward its apex. The posterior surface is convex from side to side and concave from top to bottom, allowing smooth articulation with the femoral trochlea. Average measurements in adults include a height of about 4–5 cm, a width of 4–5 cm, and a thickness of approximately 2 cm, though variations occur depending on sex, build, and activity level.

Surfaces and Borders

The patella presents two distinct surfaces, a base, an apex, and two borders. Each of these structures has anatomical and functional significance:

• Anterior surface: Rough and convex, this surface provides attachment for fibers of the quadriceps tendon and is subcutaneous, allowing it to be easily palpated.
• Posterior (articular) surface: Covered with thick articular cartilage, this surface articulates with the patellar surface of the femur and is divided by a vertical ridge into larger lateral and smaller medial facets.
• Base: The broad superior margin receives the insertion of the quadriceps femoris tendon.
• Apex: The inferior pointed end gives attachment to the patellar ligament that connects to the tibial tuberosity.
• Medial and lateral borders: Serve as attachment sites for the patellar retinacula, which stabilize the patella during movement.

Ossification and Development

Embryological Origin

The patella develops within the tendon of the quadriceps femoris muscle, classifying it as a sesamoid bone. Its formation begins in the region where the tendon passes anterior to the knee joint, allowing mechanical reinforcement and protection against frictional forces generated during movement.

Primary Ossification Center

Ossification of the patella occurs from a single primary ossification center located near the center of the cartilaginous model. Occasionally, additional accessory centers may appear and later fuse with the main ossified mass during growth. The process is influenced by mechanical stress and muscular activity during early childhood.

Timeline of Ossification

Patellar ossification typically begins between the ages of 3 and 6 years and is usually complete by puberty. The ossification pattern varies slightly between individuals and between sexes, with females often showing earlier development than males.

Stage	Approximate Age Range	Description
Cartilaginous stage	Fetal life to 2 years	Patella exists as a cartilaginous nodule within the quadriceps tendon.
Ossification onset	3–6 years	Primary ossification center appears near the middle of the cartilage.
Fusion and maturation	10–14 years	Accessory centers, if present, fuse to form a single bone mass; cartilage converts to bone.

Variations in Ossification (Bipartite and Multipartite Patella)

In some individuals, secondary ossification centers fail to fuse completely, resulting in a bipartite or multipartite patella. These variants are usually asymptomatic but may occasionally cause anterior knee pain, especially after trauma or repetitive stress. Recognition of these variants on imaging is important to differentiate them from fractures.

Articulations and Joint Relations

Articulation with the Femur (Patellofemoral Joint)

The patella articulates with the patellar surface of the femur to form the patellofemoral joint, one of the key components of the knee complex. This articulation involves the posterior surface of the patella and the trochlear groove of the femur, which is concave laterally and slightly convex medially. The patella glides superiorly during knee extension and inferiorly during flexion, maintaining continuous contact with the femoral trochlea throughout the movement.

The joint is stabilized by the alignment of the trochlear groove, the tension of the quadriceps tendon and patellar ligament, and the medial and lateral retinacula. Proper patellar tracking is essential for balanced force distribution and prevention of anterior knee pain.

Joint Capsule and Synovial Membrane

The patellofemoral joint is enclosed within the knee joint capsule. The capsule attaches along the margins of the articular surfaces of the femur and tibia and blends with the tendinous expansions of the quadriceps. The anterior portion of the capsule is reinforced by the patellar retinacula, which extend from the vastus medialis and vastus lateralis muscles to the sides of the patella.

The synovial membrane lines the internal surface of the joint capsule and reflects around the patella, forming the suprapatellar bursa above and several smaller bursae around the knee. This arrangement facilitates smooth movement of the patella during flexion and extension, minimizing friction between the quadriceps tendon and the femur.

Patellar Tracking and Movement

During knee motion, the patella acts as a dynamic lever that alters its position to maintain optimal contact with the femoral trochlea. In early flexion, the inferior part of the patella engages the trochlear groove, while deeper flexion brings the superior portion into contact. This movement pattern distributes joint pressure evenly and enhances the mechanical advantage of the quadriceps.

Abnormal tracking, such as lateral displacement, can result from muscular imbalance, shallow trochlear grooves, or malalignment of the lower limb. Such deviations are associated with conditions like patellofemoral pain syndrome or recurrent dislocation.

Attachments

Tendinous Attachments

• Quadriceps femoris tendon: The quadriceps tendon inserts into the superior aspect of the patella, forming the primary connection between the quadriceps muscle group and the bone. This attachment allows the transmission of force during extension of the knee joint.
• Patellar ligament: The continuation of the quadriceps tendon beyond the apex of the patella forms the patellar ligament, which inserts into the tibial tuberosity. This structure acts as the distal link in the extensor mechanism, transferring muscular force to the tibia.

Capsular and Retinacular Attachments

• Medial patellar retinaculum: Formed mainly by fibers of the vastus medialis and medial portion of the joint capsule, it stabilizes the patella against lateral displacement.
• Lateral patellar retinaculum: Derived from the vastus lateralis and iliotibial band, this structure provides lateral support and guides patellar motion.
• Joint capsule fibers: The capsule of the knee blends with both retinacula, providing additional reinforcement to the patellofemoral joint and anchoring the patella to the femoral condyles.

These attachments collectively ensure proper alignment of the patella during movement and contribute to knee stability. Disruption of any of these components, as seen in trauma or overuse injuries, can result in altered patellar tracking and anterior knee discomfort.

Relations with Surrounding Structures

Muscular Relations

The patella is closely associated with the quadriceps femoris muscle group, which includes the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius. These muscles converge to form the quadriceps tendon that envelops the patella and continues as the patellar ligament to insert on the tibial tuberosity. The vastus medialis, particularly its oblique fibers, plays a crucial role in maintaining medial patellar stability and preventing lateral displacement during knee extension.

Inferior to the patella lies the patellar ligament, which transmits the force of the quadriceps to extend the knee. Posteriorly, the patella lies anterior to the femoral condyles, separated by the articular cartilage and synovial fluid of the patellofemoral joint. The relationship with these muscular and ligamentous structures ensures smooth, coordinated motion and optimal joint stability during gait and physical activity.

Vascular Relations

The patella is surrounded by an extensive vascular network known as the peripatellar anastomosis. This arterial ring is formed by branches of the femoral, popliteal, and genicular arteries. Superiorly, the descending branch of the lateral circumflex femoral artery and the superior genicular arteries contribute, while inferiorly, the inferior genicular arteries join the network. These vessels ensure robust blood supply to the patella and adjacent soft tissues, supporting bone health and healing following injury.

Venous drainage parallels the arterial network, with blood flowing into the femoral and popliteal veins. The vascular pattern is clinically significant because disruption during surgery or trauma may affect bone viability and wound healing in the anterior knee region.

Nerve Supply

The sensory innervation of the patella and surrounding soft tissues is primarily provided by branches of the femoral nerve, particularly the saphenous and lateral femoral cutaneous nerves. These nerves convey sensation from the anterior aspect of the knee and play a role in proprioceptive feedback during movement. Deep structures of the joint capsule also receive innervation from articular branches of the femoral and tibial nerves.

Bursae Around the Patella

Several bursae surround the patella to reduce friction and facilitate smooth movement between soft tissue layers. The most important include:

• Prepatellar bursa: Located between the skin and anterior surface of the patella, it allows free movement of the skin during knee flexion.
• Superficial infrapatellar bursa: Found between the patellar ligament and the skin, reducing friction during kneeling.
• Deep infrapatellar bursa: Lies between the patellar ligament and the tibia, cushioning deep structures from compressive stress.
• Suprapatellar bursa: Continuous with the knee joint cavity and located between the quadriceps tendon and the femur, allowing unimpeded gliding of the tendon during flexion.

Blood Supply and Lymphatic Drainage

Arterial Supply

The arterial supply of the patella is derived from a complex anastomotic network known as the genicular anastomosis. This network includes contributions from the following arteries:

• Superior medial and superior lateral genicular arteries (branches of the popliteal artery)
• Inferior medial and inferior lateral genicular arteries (branches of the popliteal artery)
• Descending genicular artery (branch of the femoral artery)
• Descending branch of the lateral circumflex femoral artery

These vessels form a vascular ring around the patella, supplying both the osseous tissue and the surrounding soft tissues. This extensive circulation ensures adequate nourishment of the subchondral bone and periosteum, which is critical for maintaining cartilage health and bone integrity.

Venous Drainage

Venous drainage follows the arterial pathways through a corresponding peripatellar venous plexus. The veins drain superiorly into the femoral vein and inferiorly into the popliteal vein. Efficient venous return prevents edema formation in the anterior knee and supports metabolic exchange for the articular cartilage.

Lymphatic Drainage

Lymph from the patella and anterior knee structures drains into the superficial inguinal lymph nodes, located along the great saphenous vein. Deep lymphatic vessels accompanying the genicular arteries terminate in the deep inguinal nodes. This drainage pathway plays an important role in immune surveillance and the removal of metabolic waste from periarticular tissues.

Innervation

Nerves Involved

The patella itself, being a bone, has limited direct innervation; however, its surrounding structures receive sensory supply from multiple nerves that contribute to knee joint sensation and proprioception. The main nerves involved include branches of the femoral, saphenous, and tibial nerves. Small articular branches from these nerves penetrate the anterior capsule of the knee and contribute to the sensory network surrounding the patella.

• Femoral nerve: Provides articular branches that supply the anterior capsule and periosteum near the patella.
• Saphenous nerve: A cutaneous branch of the femoral nerve that supplies sensation to the medial side of the patella and anterior knee.
• Tibial nerve: Contributes deep articular branches to the posterior knee, indirectly influencing patellofemoral proprioception.
• Lateral femoral cutaneous nerve: Provides minor sensory input to the lateral region of the anterior thigh and may contribute small twigs near the lateral border of the patella.

Functional Significance of Sensory Supply

The innervation around the patella is critical for joint proprioception and coordination during dynamic movements. Sensory receptors in the surrounding retinacula, capsule, and ligaments detect stretch and pressure changes, providing feedback to maintain stability and alignment of the patella within the femoral trochlea. Disturbance of this sensory input, as seen in nerve injury or inflammation, can impair knee joint coordination and predispose to patellar maltracking or instability.

In clinical practice, regional nerve blocks targeting the femoral or saphenous nerve are used to provide analgesia for anterior knee pain or postoperative recovery following knee surgeries. Understanding the precise pattern of innervation ensures effective pain management while minimizing motor impairment.

Functions of the Patella

Biomechanical Role

The primary biomechanical role of the patella is to act as a fulcrum that enhances the leverage of the quadriceps tendon during knee extension. By increasing the angle of pull, the patella amplifies the force transmitted to the tibia, allowing efficient extension of the leg with reduced muscular effort. This mechanical advantage is crucial for activities such as walking, running, and climbing.

Additionally, the patella serves to centralize the forces exerted by the quadriceps muscle group, ensuring balanced distribution across the femoral condyles. This reduces uneven wear on the articular cartilage and enhances long-term joint stability.

Protection of the Knee Joint

The patella provides a strong bony shield to the anterior aspect of the knee joint, protecting it from direct trauma. Its superficial position over the joint capsule and synovial membrane prevents soft tissue compression during external impact. In this way, the patella acts both as a mechanical protector and a disperser of force across a broader surface area.

Lever Arm Enhancement for Quadriceps

By elevating the line of action of the quadriceps tendon away from the knee joint axis, the patella significantly lengthens the moment arm of the extensor mechanism. This configuration enables the quadriceps to produce a greater torque for knee extension. The biomechanical efficiency achieved by the patella is particularly important during early phases of extension, where the greatest resistance occurs.

Force Transmission and Stability

The patella plays a critical role in transmitting forces between the quadriceps tendon and the patellar ligament. During movement, it redirects these forces smoothly, reducing friction between the tendon and femoral condyles. Its articulation with the trochlear groove maintains joint congruity and assists in stabilizing the knee during dynamic activities.

Loss or absence of the patella, whether congenital or surgical, results in diminished quadriceps strength and reduced efficiency of knee extension. This underscores the essential mechanical and functional importance of the patella in lower limb locomotion.

Surface Anatomy and Palpation

Identification in Clinical Examination

The patella is a prominent superficial structure located at the anterior aspect of the knee joint, easily palpable through the skin. During clinical examination, it serves as an important landmark for assessing knee alignment, swelling, and joint effusion. In full extension, the patella lies high on the femoral condyles and becomes more mobile due to relaxation of the quadriceps tendon. As the knee flexes, the patella descends and fits into the trochlear groove of the femur, where its movement can be felt beneath the skin.

Clinicians commonly assess the patella for tenderness, position, and mobility. The superior border corresponds to the attachment of the quadriceps tendon, while the inferior apex marks the upper limit of the patellar ligament. Palpation of these borders allows identification of soft tissue inflammation, tendinopathy, or structural deformities.

Movements During Knee Flexion and Extension

The patella moves along the femoral trochlea in response to knee motion. During extension, it glides upward and slightly laterally, while during flexion, it moves downward and medially into the intercondylar groove. This dynamic movement is controlled by the quadriceps muscle group and the medial and lateral patellar retinacula. Proper patellar tracking ensures even distribution of joint stress and prevents cartilage wear.

Abnormal motion, such as excessive lateral deviation or tilting, can be detected through palpation and dynamic tests. The patellar glide test and apprehension test are clinical maneuvers used to evaluate patellar mobility and potential instability. These assessments provide valuable information for diagnosing conditions like patellar dislocation or maltracking.

Radiological Anatomy

X-ray Appearance and Landmarks

On plain radiographs, the patella appears as a triangular bone with a distinct cortical outline and well-defined articular surface. Standard radiographic views for evaluating the patella include the anteroposterior, lateral, and axial (skyline or Merchant) projections. The lateral view shows the patella’s relationship with the femur, while the skyline view highlights the patellofemoral articulation and helps detect alignment abnormalities.

• Lateral view: Demonstrates the height and position of the patella relative to the femur. A high-riding patella is termed patella alta, while a low-lying one is known as patella baja.
• Skyline (axial) view: Visualizes the articular facets and trochlear groove, useful for detecting cartilage defects and patellar tilt.
• Anteroposterior view: Helps identify bony irregularities, fractures, or ossification variations.

CT and MRI Imaging Features

Computed tomography (CT) provides detailed information on patellar alignment, tilt, and subluxation, making it useful for preoperative planning and evaluation of patellofemoral disorders. Magnetic resonance imaging (MRI) offers superior soft tissue visualization, allowing assessment of cartilage, ligaments, retinacula, and bone marrow. MRI is particularly valuable in detecting chondromalacia patellae, bone edema, and retinacular injuries.

The articular cartilage of the patella appears smooth and uniform on MRI, while signal irregularities suggest degenerative or traumatic damage. Cross-sectional imaging also helps identify bipartite patella and distinguish it from acute fractures by demonstrating well-corticated margins and lack of associated bone marrow edema.

Normal Variants on Imaging

Several anatomical variants of the patella can be visualized radiographically. The most common is the bipartite patella, typically located at the superolateral corner and separated by a fibrous or cartilaginous junction. Other variants include multipartite patella and accessory ossicles near the patellar borders. Recognition of these normal variants is essential to prevent misdiagnosis of fractures, especially in trauma cases.

Imaging also helps assess patellar position using indices such as the Insall-Salvati ratio, which compares patellar tendon length to patellar height. This ratio assists clinicians in diagnosing positional abnormalities that affect knee biomechanics and predispose to anterior knee pain.

Variations and Anomalies

Bipartite and Multipartite Patella

Bipartite and multipartite patellae are developmental variations that occur when secondary ossification centers of the patella fail to fuse completely during growth. The bipartite type is more common, representing two distinct bony segments usually connected by fibrocartilaginous tissue. The superolateral region of the patella is the most frequent site of separation, observed in up to 2% of the population.

Although typically asymptomatic and discovered incidentally on imaging, these variants may cause anterior knee pain after trauma or repetitive strain. On radiographs, bipartite patella appears as a well-corticated accessory fragment distinct from a fracture, as there is no associated bone marrow edema or sharp cortical disruption. Recognition of this normal variant is crucial for accurate diagnosis and management.

Congenital Absence of the Patella

Congenital absence, or patellar aplasia, is a rare anomaly often associated with syndromic conditions such as nail-patella syndrome or arthrogryposis. In these cases, the absence or hypoplasia of the patella is accompanied by musculoskeletal abnormalities, including underdeveloped quadriceps muscles and restricted knee movement. Patients typically present with reduced knee extension strength, instability, and altered gait.

Radiographic and MRI imaging confirm the diagnosis by showing a lack of ossified patellar tissue. Management is primarily conservative, focusing on strengthening surrounding musculature and improving joint function through physiotherapy. Surgical options are limited and reserved for severe functional impairment.

Patellar Shape and Size Variations

The patella exhibits considerable morphological variation among individuals. Differences in shape include oval, circular, or triangular forms, while size variations depend on sex, age, and activity level. A smaller or flatter patella may predispose to instability and altered patellofemoral mechanics. These anatomical differences are important considerations in orthopedic planning, prosthetic design, and radiological evaluation.

Wiberg’s classification categorizes patellae based on articular facet shape and proportion into three primary types: Type I with equally sized facets, Type II with a smaller medial facet, and Type III with a markedly reduced medial facet. Type III patella is most associated with lateral tracking and instability symptoms.

Applied Anatomy and Clinical Significance

Patellar Fractures

Patellar fractures are common injuries resulting from direct trauma to the anterior knee or sudden, forceful contraction of the quadriceps muscle. They can be transverse, vertical, comminuted, or osteochondral in pattern. Clinical features include pain, swelling, inability to extend the knee, and palpable discontinuity in the bone.

Radiographic evaluation using anteroposterior and lateral views confirms the diagnosis. Treatment depends on fracture type and displacement; nondisplaced fractures are treated conservatively with immobilization, whereas displaced or comminuted fractures often require surgical fixation using tension band wiring or partial patellectomy.

Patellar Dislocation and Subluxation

Dislocation of the patella occurs when it moves out of the trochlear groove, most commonly laterally, due to trauma or congenital instability. Predisposing factors include a shallow trochlear groove, valgus alignment of the knee, and weakness of the vastus medialis obliquus. Subluxation refers to partial displacement with spontaneous reduction.

Clinically, dislocation presents with pain, swelling, and a visible lateral shift of the patella. Reduction is usually achieved by gentle extension of the knee. Long-term management includes physiotherapy to strengthen the quadriceps and, in recurrent cases, surgical realignment of the extensor mechanism.

Patellofemoral Pain Syndrome

Patellofemoral pain syndrome, or “runner’s knee,” is a common overuse injury characterized by anterior knee pain exacerbated by activities such as climbing stairs, squatting, or prolonged sitting. It is caused by malalignment, overuse, or muscular imbalance affecting patellar tracking. Examination reveals tenderness around the patellar margins and pain during compression against the femur.

Treatment focuses on physiotherapy, emphasizing strengthening of the vastus medialis, correction of biomechanical imbalances, and use of supportive taping or orthotics. Surgical intervention is reserved for persistent cases with structural abnormalities.

Surgical and Orthopedic Considerations

Open Reduction and Internal Fixation (ORIF)

Open reduction and internal fixation are standard surgical methods used to treat displaced patellar fractures. The goal of ORIF is to restore the integrity of the extensor mechanism and ensure early mobilization of the knee joint. Tension band wiring, screw fixation, or plate fixation are the most commonly employed techniques, depending on the fracture pattern. Proper anatomical reduction is essential to maintain the smooth articulation between the patella and femoral trochlea, reducing the risk of post-traumatic arthritis.

Postoperative rehabilitation focuses on controlled mobilization to prevent stiffness and promote healing. Early physiotherapy and gradual strengthening of the quadriceps are crucial for restoring knee extension and functional recovery.

Patellar Resurfacing in Knee Arthroplasty

In total knee arthroplasty, patellar resurfacing may be performed to improve postoperative outcomes and reduce anterior knee pain. The procedure involves removing the damaged articular cartilage from the posterior surface of the patella and replacing it with a polyethylene prosthetic component. The decision to resurface the patella is individualized, based on factors such as cartilage condition, patient age, and activity level.

Proper alignment and thickness restoration are critical to avoid complications like maltracking or excessive patellar pressure. Post-surgical evaluation ensures congruence of the patellar implant with the femoral component for smooth articulation and long-term durability.

Reconstruction of Patellar Tendon

Patellar tendon rupture is a serious injury that disrupts the continuity of the extensor mechanism, leading to loss of active knee extension. Surgical repair or reconstruction is typically required, especially in complete tears. Autografts from the hamstring tendons or allografts may be used when direct end-to-end repair is not feasible. Postoperative management involves immobilization followed by progressive physiotherapy to regain strength and flexibility.

Failure to repair the tendon properly can result in chronic weakness, patella alta, and impaired knee mechanics. Thus, early diagnosis and meticulous surgical technique are vital for optimal functional recovery.

Arthroscopic Procedures Involving the Patella

Arthroscopy is widely used for diagnosing and managing patellofemoral disorders. Common arthroscopic procedures include debridement of chondral lesions, lateral release for correcting patellar maltracking, and cartilage restoration techniques. Arthroscopy offers the advantage of minimal invasiveness, shorter recovery time, and reduced postoperative complications compared to open surgery.

In cases of chronic anterior knee pain or instability, arthroscopy allows direct visualization of the patellofemoral articulation, enabling targeted treatment of soft tissue abnormalities while preserving joint function.

Comparative and Evolutionary Anatomy

Patella in Other Mammals

The patella is present in most quadrupedal mammals, serving a similar biomechanical role in enhancing the efficiency of knee extension. However, its size and degree of ossification vary widely among species, depending on locomotive demands. In animals such as dogs and horses, the patella assists in powerful limb extension for running and jumping, whereas in smaller mammals like rodents, it remains relatively small or cartilaginous.

Some species, including certain reptiles and amphibians, lack a true ossified patella, instead possessing a fibrous or cartilaginous structure embedded within the tendon. This variation reflects evolutionary adaptation to different modes of locomotion and joint stress requirements.

Evolutionary Adaptations in Humans

In humans, the patella has evolved to accommodate upright posture and bipedal locomotion. The increased demands of weight-bearing and extended knee activity necessitated a robust sesamoid bone capable of optimizing the leverage of the quadriceps tendon. The human patella is relatively larger and thicker than that of most other primates, contributing to enhanced stability and energy efficiency during walking and running.

Evolutionary studies suggest that the patella first appeared in early tetrapods and gradually ossified in mammals and birds, where joint mechanics required improved extensor leverage. The human patella, with its pronounced articular surface and well-defined facets, represents a culmination of these adaptations for efficient locomotion and upright stance.

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